This invention relates to debeading or trimming of weld flash inside a butt-welded plastic pipe and more particularly to a tool that can be used with hard plastics such as PVC, PVDF, polypropylene and the like. Plastic pipes and pipe liners typically are made in standard lengths, such as 20 feet or 40 feet, and are interconnected end-to-end to make a long pipe string.
Butt welding of plastic pipe produces a weld bead or flash that is preferably removed before the pipe is placed in service for conveying liquids to reduce flow restriction and reduction, turbulence wear, biofilm/bacteria entrapment and potential for blockages forming at the joints. Plastic pipes are also used as conduit for cable, and, again, it is desirable to remove the weld flash before attempting to pull cable into the butt-welded pipe string.
In the past, such pipes have been made of polyethylene, which is a relatively soft thermoplastic that can be readily butt-welded and easily debeaded. A tool known as the Bead Trimmer II™ has been made and sold by R & L Manufacturing Inc. of Camas, Wash. The tool includes a bead trimmer head assembly that mounts on one end of a series of interconnected torque tubes and is pushed into the butt-welded pipe until the internal bead or weld flash is contacted. The head assembly has a central shaft that couples to the torque tube end and has a centering disk sized to the pipe for retaining the head assembly centered in the pipe as it is inserted. A gauge mounted on the periphery of the centering disk contacts the bead when the tool reaches the bead. When contact is made, the operator manually rotates a T-shaped bar mounted at the opposite end of the torque tube string to rotate a cutter around a full circle inside of the pipe. The cutter includes a fixed blade that extends lengthwise along the sidewall of the pipe, aligned with the gauge so that, when the gauge contacts the weld flash or bead, the blade straddles the bead. The blade has an edge that is beveled to cut into the bead when rotated until locating registers at each end of the blade holder contact the inner wall of the pipe, at which point the blade holder maintains a constant cutting depth of the blade edge. Continued rotation of the head assembly cuts the bead away from the pipe wall. When this action is completed, the head assembly is withdrawn from the pipe. Several hooks distributed radially around the downstream end of the head assembly engage the cut-away bead and drag it from the pipe.
Recent formulations of PVC, such as C-900 and C-905 fusible PVC, have enabled butt-welding PVC pipes. The fusion methods developed for this material likewise produces a weld flash or bead, which it is also desirable to remove. PVC is much harder than polyethylene; so hard, in fact, that the Bead Trimmer II™ is incapable of cutting the weld flash or bead. Other plastics that are similarly hard include PVDF and polypropylene.
Accordingly, a need remains for a way to debead butt-welded pipe made of PVC, PVDF, polypropylene and other similarly hard plastics.